1. Field of the Invention
The present invention relates to a closed rotary compressor and, more particularly, to the closed rotary compressor of a type suited for use in a refrigerator, an air-conditioner or the like for compressing refrigerant gas.
2. Description of Related Art
The closed rotary compressor is well known in the art, an example of which is shown in FIGS. 10 and 11 in longitudinal and transverse sectional representations, respectively, for discussion of the prior art believed to be relevant to the present invention.
The closed rotary compressor shown in FIGS. 10 and 11 includes a generally cylindrical sealed vessel 1 tightly closed at its opposite ends and accommodating therein an electric motor 2 comprised of a stator 2-1 and a rotor 2-2. This sealed vessel 1 also accommodates therein a compressor mechanism 3 positioned beneath the electric motor 2 and adapted to be driven by the electric motor 2. While the compressor mechanism 3 is driven, a refrigerant introduced into the compressor mechanism 3 from an intake port 5 through an accumulator (not shown) and an intake tube 4 is compressed. The resultant compressed refrigerant is discharged into the sealed vessel 1 through an outlet port 6 and then therefrom to a refrigerating circuit through a discharge tube 7 disposed at an upper portion of the sealed vessel 1.
The compressor mechanism 3 of the prior art rotary compressor comprises, as best shown in FIGS. 10 and 11, a shaft 8 adapted to be driven by the electric motor 2 and having its upper and lower ends rotatably received by main and auxiliary bearings 9 and 11, respectively, a generally intermediate portion of said shaft 8 extending through a cylinder 10 fixed in position inside the sealed vessel 1. A crank (eccentric portion) 12 is fixedly mounted on, or otherwise formed integrally with, a portion of the shaft 8 situated within the cylinder 10 for rotation together therewith. A ring-shaped roller 13 is operatively positioned between an inner wall surface of the cylinder 10 and an outer peripheral surface of the crank 12 and will, while the shaft 8 is driving, undergo a planetary motion.
As best shown in FIG. 11, the cylinder 10 has a radial groove 22 defined therein so as to extend in a direction radially thereof, and a slidable radial vane 14 is accommodated within the radial groove 22 for movement within the radial groove 22 in a direction towards and away from the roller 13. This slidable radial vane 14 is normally biased by a biasing spring 15 in one direction with a radially inward end thereof held in sliding contact with an outer peripheral surface of the ring-shaped roller 13, thereby dividing the volume of the cylinder 10 into volumetrically variable, suction and compression chambers 16 and 17 that are defined, respectively on leading and trailing sides of the slidable radial vane 14 with respect to the direction of rotation of the shaft 8.
According to the prior art closed rotary compressor shown in FIGS. 10 and 11, refrigerant gas is, during the planetary motion of the ring-shaped roller 13 accompanying an eccentric rotation of the crank 12 rigid with the shaft 8, sucked into the suction chamber 16 through the intake port 5 and then compressed before it is discharged through a discharge port 19. In order to facilitate a sliding motion of the ring-shaped roller 13 relative to the inner wall surface of the cylinder 10 and the radial inner end of the slidable radial vane 14 and also a sliding motion of the radial vane 14 within the radial groove 22, a quantity of lubricating oil is accommodated within the sealed vessel 1 at a bottom portion 20 thereof. The lubricating oil is sucked up by an oil pump 21 mounted on the lower end of the shaft 8 to oil various sliding elements within the compressor mechanism 3.
Of the various sliding elements used in the compressor mechanism 3, the slidable radial vane 14 when noticeably worn out creates a detrimental problem. As is well known to those skilled in the art, the slidable radial vane 14 is frictionally engaged not only with the ring-shaped roller 13, but also with side surfaces defining the radial groove 22 in the cylinder 10. Specifically, by the biasing force of the biasing spring 15 and a back pressure acting on the trailing surface of the slidable radial vane 14, the radial inner end of the slidable radial vane 14 is constantly held in frictional engagement with the ring-shaped roller 13 and, also, by the effect of a pressure difference between the suction and compression chambers 16 and 17, opposite side surfaces of the slidable radial vane 14 are alternately held in frictional engagement with the corresponding side surfaces defining the radial groove 22. Unlike other sliding elements such as, for example, the shaft 8 and its bearing mechanism, the slidable radial vane 14 is not lubricated by the lubricating oil supplied directly by the oil pump 21, but is lubricated by an oil component, contained in the refrigerant being compressed, and/or an oil leaking from roller ends. The quantity of the oil available from the refrigerant being compressed and leaking from the roller ends is indeed insufficient for lubricating the slidable radial vane 14 and its surrounding parts satisfactorily. In addition, considering that the refrigerant when compressed reaches an elevated temperature, the slidable radial vane 14 in contact with the refrigerant being compressed is heated and is therefore susceptible to an accelerated frictional wear.
In order to eliminate the above discussed problems, Japanese Laid-open Patent Publication (unexamined) No. 57-173589 suggests the use of an oil injector mechanism 51 as shown in FIG. 12.
The oil injector mechanism 51 includes an oil supply tube 52 composed of a capillary tube and installed at a lower portion of the cylinder 10, with one end thereof immersed in the lubricating oil such that the oil supply tube 52 communicates with the intake port 5. The oil injector mechanism 51 also includes a valve 53 for opening and closing an upper open end of the oil supply tube 52 by a pressure difference, and a coil spring 57 for biasing the valve 53 downwardly.
The biasing force of the coil spring 57 is so chosen as to be greater than the pressure in the sealed vessel 1 during a normal operation but smaller than the pressure in the sealed vessel 1 during an abnormal operation in which the pressure in the sealed vessel 1 is abnormally high. During the abnormal operation, the ring-shaped roller 13 and the slidable radial vane 14 are likely to wear due to a high load. In order to prevent the roller 13 and the vane 14 from wearing, the lubricating oil stored at the bottom of the sealed vessel 1 is introduced into the intake port 5 by means of a pressure difference and is mixed with the refrigerant gas to lubricate the surfaces of the roller 13 and the vane 14. On the other hand, during the normal operation, this construction prevents high-temperature oil from entering the intake path to lower the efficiency of the compressor.
For the refrigerant used in the refrigerating system including the closed rotary compressor, dichlorodifluoromethane (hereinafter referred to as "CFC 12") or hydrochlorofluoromethane (hereinafter referred to as "HCFC 22") is generally used. On the other hand, the lubricating oil in the compressor mechanism 3 is generally either a mineral oil of naphthene or that of paraffin having a solubility with CFC 12 or HCFC 22.
Since the refrigerant and the lubricating oil circulate directly within the sealed vessel 1, the various component parts of the compressor mechanism 3 must have a sufficient resistance to wear.
Apart from the above, it has come to be recognized that the emission of Freon, used as the refrigerant into the atmosphere does not only seriously damage the ozone layer, but brings about global ecological damage. In view of this, an international agreement has been made to step by step freeze for some years ahead and eventually abolish the production of CFC 12 and HCFC 22. Under these circumstances, as a substitute refrigerant, 1,1,1,2-tetrafluoroethane (hereinafter referred to as "HFC 134a"), 1,1 difluoroethane (hereinafter referred to as "HFC 152a" and hydrodifluoromethane (hereinafter referred to as "HFC 32") or a mixture thereof have been developed.
While the substitute refrigerant such as HFCs 134a, 152a and 32 is less likely to result in damage of the ozone layer, it lacks a solubility with such a mineral lubricant as hitherto used in combination with the CFC 12 or HCFC 22. For this reason, where the substitute refrigerant is to be used in the refrigerating system, attempts have been made to use such a lubricant oil of ether, ester or fluorine family which has a compatibility with the substitute refrigerant.
However, where a combination of any one of the HFCs 134a, 152a and 32 in place of any of the CFC 12 and HCFC 22 with either polyalkylene glycol oil or polyester oil having a compatibility with such substitute refrigerant is used in the refrigerant compressor, it has been found that the resistance to frictional wear of such metallic material as FC25, special cast iron, sintered alloy and stainless steel used for sliding elements in the refrigerant compressor tends to be lowered and, therefore, the refrigerant compressor cannot be operated stably for a long period of time. This is because of the following reasons.
So long as the conventional CFC 12 or HCFC 22 is used as the refrigerant, chlorine atoms contained in the conventional refrigerant react with Fe atoms contained in the metal matrix to form a film of ferric chloride that is excellent in resistance to frictional wear. However, in the case of the substitute refrigerant such as HFC 134a, HFC 152a or HFC 32, no chlorine atoms exist in this compound and, therefore, no lubricating film such as a film of ferric chloride is formed, accompanied by a reduction in lubricating action.
In addition, while the conventional mineral oil used as a lubricant contains a cyclic compound and has therefore a relatively high capability of forming an oil film, the lubricating oil compatible with the substitute refrigerant is composed mainly of a chain compound and is therefore unable to form a required oil film under severe sliding conditions, accompanied by an accelerated reduction in resistance to frictional wear.
As discussed above, the refrigerant compressor operable with the substitute refrigerant and the lubricating oil compatible with this substitute refrigerant is often placed under severe sliding conditions not only during a high load drive, but also during a normal drive and, therefore, the frictional wear of the vane and roller has become more pronounced.
In order to cope with the above-described problems, the solution suggested in the previously discussed publication No. 57-173589 may be so modified as to perform oil injection even during the normal drive by weakening the biasing force of the spring or by removing the spring. In this case, however, the intake port is supplied with high-temperature oil, which in turn overheats the refrigerant introduced into the compressor, thus lowering the efficiency of the compressor.